I dunno about you, but I'd love to see a movie based on Cranium Command.
Space Mountain or Thunder Mountain might make good movies, although they don't have well-defined stories behind them like HM. Then again, Pirates didn't have a well-defined story behind it either, but they managed to turn it into a fantastic movie.
Splash Mountain is, itself, based on a movie - Song of the South. But since SOTS has been hidden away in shame for 40 years, maybe Disney could take the cartoon characters of Brer Rabbit, Fox, and Bear, and make an entirely new animated feature out of them that wouldn't embarass them to no end.
Kilamanjaro Safari at AK has a wonderful storyline and characters that could be fleshed out into a movie.
The characters from the late, lamented attraction Horizons would have made a terrific movie.
A full-length movie with Figment would be pretty cool.